Device And Method Of Combusting Solid Fuel With Oxygen

ABSTRACT

The present invention is a method of combustion of a solid fuel stream with oxygen. The present invention includes introducing a first stream, comprising a first portion of substantially pure oxygen, into a first conduit. The present invention includes introducing a second stream, comprising a solid fuel stream and a conveying media, into a second conduit, wherein the second conduit is concentric with, and surrounding, the first conduit. The present invention includes introducing a third stream, comprising a second portion of substantially pure oxygen, into a third conduit, wherein the third conduit is concentric with, and surrounding, the first conduit and the second conduit. The present invention includes igniting the first stream, the second stream, and the third stream as they exit the first conduit, the second conduit and the third conduit, in such a way as to create a flame. The present invention includes introducing a fourth stream, comprising a first portion of ballast gas, into a fourth conduit, wherein the fourth conduit is concentric with, and surrounding, the first conduit, the second conduit, and the third conduit. The present invention includes introducing a fifth stream, comprising a second portion of ballast gas, into a fifth conduit, wherein the fifth conduit is concentric with, and surrounding, the first conduit, the second conduit, the third conduit and the fourth conduit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/050,515, filed May 5, 2008, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a method combusting solid fuel with oxygen.

BACKGROUND

With the increasingly stringent environmental restrictions, particularlyin terms of the production of CO₂ and NO_(x), the combustion of a fuelusing oxygen or a high-oxygen-content gas is becoming increasinglyattractive for the combustion of fossil fuels. However, the conventionalcombustion devices using air as oxidizer do not always have thegeometry, nor the requisite materials, for operating with oxygen or ahigh-oxygen-content gas. This is because the absence of the nitrogenballast in high-oxygen or all-oxygen combustion significantly modifiesthe heat transfer modes, the species concentrations, and the pressureconditions in the combustion chamber.

In order to operate with all-oxygen combustion in these installations,one proposed solution is to reinject flue gas produced by the saidcombustion or another combustion to partly make up for the absence ofnitrogen. This procedure serves to avoid a high production of NO_(x) dueboth to the absence of nitrogen, and also to a lower flame temperaturethan in all-oxygen combustion. However, the reinjected flue gas oftennullifies the benefits of oxycombustion, such as, in particular, lowerdownstream flue gas treatment, efficiency increase due to hightemperature combustion process etc.

Coal is a major source of fuel in the world. Different devices andmethods are available today to combust coal. Coal is usually combustedwith air or with a mixture of oxygen and flue gases (‘synthetic air’).Prior art exists today where oxygen is mixed with flue gas andintroduced into the combustor. Separate injection of fuel, oxygen, andflue gas have been proposed for gaseous and liquid fuels, where themixing of fuel and oxidants are relatively easy. Also, there is noconveying media required to transport gaseous or liquid fuels, whereassuch a conveying media is required for a solid fuel combustion.

Synthetic air requires mixing of oxygen with flue gases and there isless flexibility with respect to the oxygen to flue gas ratio (typicallyabout 18% to about 40%) due to safety and technical issues. Syntheticair also dilutes the combustion which makes it difficult to burn lowquality coal.

Therefore, there exists a need in the industry for a solution that willallow the above problems to be circumvented.

SUMMARY

The present invention is a method of combustion of a solid fuel streamwith oxygen. The present invention includes introducing a first stream,comprising a first portion of substantially pure oxygen, into a firstconduit. The present invention includes introducing a second stream,comprising a solid fuel stream and a conveying media, into a secondconduit, wherein said second conduit is concentric with, andsurrounding, said first conduit. The present invention includesintroducing a third stream, comprising a second portion of substantiallypure oxygen, into a third conduit, wherein said third conduit isconcentric with, and surrounding, said first conduit and said secondconduit. The present invention includes igniting said first stream, saidsecond stream, and said third stream as they exit said first conduit,said second conduit and said third conduit, in such a way as to create aflame. The present invention includes introducing a fourth stream,comprising a first portion of ballast gas, into a fourth conduit,wherein said fourth conduit is concentric with, and surrounding, saidfirst conduit, said second conduit, and said third conduit. The presentinvention includes introducing a fifth stream, comprising a secondportion of ballast gas, into a fifth conduit, wherein said fifth conduitis concentric with, and surrounding, said first conduit, said secondconduit, said third conduit and said fourth conduit. The presentinvention includes surrounding said with said fourth stream and saidfifth stream, as they exit said fourth conduit and said fifth conduit.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, and inwhich:

FIG. 1 is a schematic representation of one embodiment of the presentinvention.

FIG. 2 is a schematic representation of another embodiment of thepresent invention, indicating the fourth stream being divergent and thefifth stream being convergent.

FIG. 3 is a schematic representation of another embodiment of thepresent invention, indicating the swirling devices in the fourth andfifth streams, as well as the dampers.

FIG. 4 is a schematic representation of another embodiment of thepresent invention, indicating the control system and swirling devices inthe 2^(nd) stream.

DESCRIPTION OF PREFERRED EMBODIMENTS

The proposed method detaches the oxygen and flue gas introduction andimproves the flexibility of having a broad range to the oxygen to fluegas ratio. The proposed method takes advantage of oxycombustion togenerate high temperatures, thereby accelerating the devolatilization ofcoal and thus the combustion of the coal. This dilution happens onlyafter the combustion with pure oxygen to maintain the required furnacewall temperature.

The present invention proposes an innovative device and method tocombust solid fuel such as coal with pure oxygen. Fuel, oxygen, and fluegases are introduced separately into the boiler via the proposeddevice/burner. This device enables independent flow control of flue gasand oxygen compared to the state of the art, where oxygen and flue gasare mixed then introduced. The proposed method enhances thedevolatilization of fuel with the use of pure oxygen and thus improvesthe combustion process. This promotes the utilization of low qualitycoals which are difficult to burn with air or synthetic air withexisting technologies.

Turning to FIG. 1, injector 100 is presented. Coal is introduced throughcoal pipe 102 (second stream) of the burner, with a conveying media,preferably recycled flue gas (either alone or combined with oxygen). Thecoal may be injected with or without inducing a swirl, depending on thequality of the coal, flame length required etc. A first portion of thesubstantially pure oxygen is introduced through lance 101 (firststream), to improve the flame stability. A second portion ofsubstantially pure oxygen is introduced into oxygen orifice 103 (thirdstream). Oxygen orifice 103 (third stream) surrounds coal pipe 102(second stream) and is introduced to facilitate the complete combustionof coal in an oxygen environment. First recycled flue gas stream 104(fourth stream) and second recycled flue gas stream 105 (fifth stream)are introduced on the outer perimeter of oxygen orifice 103 (thirdstream), thereby maintaining the furnace temperature to an acceptablelevel. The oxyflame is diluted to the required extent with recycled fluegases (104, 105) (fourth stream and fifth stream) around the pure oxygeninjection (103).

Turning to FIG. 2, injector 200 is presented. Coal is introduced throughcoal pipe 202 (second stream) of the burner, with a conveying media,preferably recycled flue gas (either alone or combined with oxygen). Thecoal may be injected with or without inducing a swirl, depending on thequality of the coal. A first portion of the substantially pure oxygen isintroduced through lance 201 (first stream), to improve the flamestability. A second portion of substantially pure oxygen is introducedinto oxygen orifice 203 (third stream). Oxygen orifice 203 (thirdstream) surrounds coal pipe 202 (second stream) and is introduced tofacilitate the complete combustion of coal in an oxygen environment.First recycled flue gas stream 204 (fourth stream) and second recycledflue gas stream 205 (fifth stream) are introduced on the outer perimeterof oxygen orifice 203 (third stream), thereby maintaining the furnacetemperature to an acceptable level. The oxyflame is diluted to therequired extent with recycled flue gases (204, 205) (fourth stream andfifth stream) around the pure oxygen injection (203). In thisembodiment, in order to improve the mixing of the dilutant/flue gases(204, 205) with the flame (201, 202, 203) the flue gases (204, 205) canbe injected in a non-axial fashion as shown in FIG. 2. The majority ofthe flue gases are preferably injected at an angle that is divergentfrom the axial centreline CL of injector 200, with a minor flow beinginjected at an angle that is convergent with the axial centreline CL.

Turning to FIG. 3, injector 300 is presented. Coal is introduced throughcoal pipe 302 (second stream) of the burner, with a conveying media,preferably recycled flue gas (either alone or combined with oxygen). Thecoal may be injected with or without inducing a swirl, depending on thequality of the coal, flame length required etc. In order to furtherimprove the combustibility of very low quality solid fuel, a secondaryfuel such as oil or gas may be injected along with the solid fuel intocoal pipe 302 (second stream). It is also possible to valorize lowquality secondary fuel when the solid fuel does not need the assistanceof the secondary fuel (i.e. good quality solid fuel). A first portion ofthe substantially pure oxygen is introduced through lance 301 (firststream), to improve the flame stability. A second portion ofsubstantially pure oxygen is introduced into oxygen orifice 303 (thirdstream). Oxygen orifice 303 (third stream) surrounds coal pipe 302(second stream) and is introduced to facilitate the complete combustionof coal in an oxygen environment. First recycled flue gas stream 304(fourth stream) and second recycled flue gas stream 305 (fifth stream)are introduced on the outer perimeter of oxygen orifice 303 (thirdstream) thereby maintaining the furnace temperature to an acceptablelevel. First recycled flue gas stream 304 (fourth stream) may beintroduced with a clockwise swirl A or a counter-clockwise swirl B.Second recycled flue gas stream 305 (fifth stream) may be introducedwith a clockwise swirl C or a counter-clockwise swirl D.

The oxyflame is diluted to the required extent with recycled flue gases(304, 305) around the pure oxygen injection (303). In this embodiment,in order to improve the mixing of the dilutant/flue gases (304, 305)with the flame (301, 302, 303) the flue gases (304, 305) can be injectedin a non-axial fashion as shown in FIG. 3?. The majority of the fluegases are preferably injected at an angle that is divergent from theaxial centreline CL of injector 300, with a minor flow being injected atan angle that is convergent with the axial centreline CL.

In order to further improve the mixing of the flue gases (304, 305) withthe flame (301, 302, 303), swirl can be introduced into the flue gases(304, 305). As shown in FIG. 3, opposite swirls are preferably inducedin the two zones of flue gas injection by element 306. The flow betweenthe two flue gas injection zones can be changed with damper 307positioned between these zones.

Turning to FIG. 4, injector 400 is presented. Coal is introduced throughcoal pipe 402 (second stream) of the burner, with a conveying media,preferably recycled flue gas (either alone or combined with oxygen). Thecoal may be injected with or without inducing a swirl, depending on thequality of the coal, flame length required etc. A first portion of thesubstantially pure oxygen is introduced through lance 401 (firststream), to improve the flame stability. A second portion ofsubstantially pure oxygen is introduced into oxygen orifice 403 (thirdstream). Oxygen orifice 403 (third stream) surrounds coal pipe 402(second stream) and is introduced to facilitate the complete combustionof coal in an oxygen environment. First recycled flue gas stream 404(fourth stream) and second recycled flue gas stream 405 (fifth stream)are introduced on the outer perimeter of oxygen orifice 403 (thirdstream), thereby maintaining the furnace temperature to an acceptablelevel. The oxyflame is diluted to the required extent with recycled fluegases (404, 405) around the pure oxygen injection (403). In thisembodiment, in order to improve the mixing of the dilutant/flue gases(404, 305) with the flame (401, 402, 403) the flue gases (404, 405) canbe injected in a non-axial fashion as shown in FIG. 4. The majority ofthe flue gases are preferably injected at an angle that is divergentfrom the axial centreline CL of Injector 400, with a minor flow beinginjected at an angle that is convergent with the axial centreline CL.

In order to further improve the mixing of the flue gases (404, 405) withthe flame (401, 402, 403), swirl can be introduced into the flue gases(404, 405). As shown in FIG. 4, opposite swirls are preferably inducedin the two zones of flue gas injection by element 406. The flow betweenthe two flue gas injection zones can be changed with damper 407positioned between these zones.

A control system 408 may automatically adjust the combustiondisturbances that may be caused with changing quality of coal or otherpurturbences. The staging of oxygen between lance 401 and surroundingthe coal pipe 402 can be changed along with the distribution of recycledflue gases in the two surrounding zones (404, 405). The combustioncharacteristics can be measured by monitoring the flue gases (409) andthe information then being fed to the control system.

In another embodiment, in order to improve the efficiency of thecombustion process, the oxygen can be preheated to a higher temperaturebefore introduction into the burner. The heat source may be the flue gasexiting the boiler, or any other locally available heat source, or heatsource that is part of the present process. It is also envisioned thatthe oxygen streams (101,201,301,401, 103,203,303,403) can be injected inmany different ways such as, but not limited to, axial, radial,convergent, divergent, with and with out swirl or the combination ofsome of these.

Illustrative embodiments have been described above. While the method inthe present application is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings, and have been herein described in detail. Itshould be understood, however, that the description herein of specificembodiments is not intended to limit the method in the presentapplication to the particular forms disclosed, but on the contrary, themethod in the present application is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of themethod in the present application, as defined by the appended claims.

It will, of course, be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but,would nevertheless, be a routine undertaking for those of ordinary skillin the art, having the benefit of this disclosure.

1. A method of combustion of a solid fuel stream, comprising: a)introducing a first stream, comprising a first portion of substantiallypure oxygen, into a first conduit, b) introducing a second stream,comprising a solid fuel stream and a conveying media, into a secondconduit, wherein said second conduit is concentric with, andsurrounding, said first conduit, c) introducing a third stream,comprising a second portion of substantially pure oxygen, into a thirdconduit, wherein said third conduit is concentric with, and surrounding,said first conduit and said second conduit, d) igniting said firststream, said second stream, and said third stream as they exit saidfirst conduit, said second conduit and said third conduit, in such a wayas to create a flame, e) introducing a fourth stream, comprising a firstportion of ballast gas, into a fourth conduit, wherein said fourthconduit is concentric with, and surrounding, said first conduit, saidsecond conduit, and said third conduit, and f) introducing a fifthstream, comprising a second portion of ballast gas, into a fifthconduit, wherein said fifth conduit is concentric with, and surrounding,said first conduit, said second conduit, said third conduit and saidfourth conduit.
 2. The method of claim 1, wherein said conveying mediais recycled flue gas, substantially pure oxygen, or a combination. 3.The method of claim 1, wherein said solid fuel is coal.
 4. The method ofclaim 1, wherein said first portion of ballast gas is recycled flue gas.5. The method of claim 1, wherein said second portion of ballast gas isrecycled flue gas.
 6. The method of claim 1, wherein said first conduithas a longitudinal axis, wherein said fourth conduit directs said firstportion of ballast gas flow in a direction essentially divergent fromsaid longitudinal axis.
 7. The method of claim 1, wherein said firstconduit has a longitudinal axis, wherein said fifth conduit directs saidsecond portion of ballast gas flow in a direction essentially convergentfrom said longitudinal axis.
 8. The method of claim 1, wherein saidfourth conduit creates a clockwise swirl in said first portion ofballast gas flow.
 9. The method of claim 1, wherein said fourth conduitcreates a counter-clockwise swirl in said first portion of ballast gasflow.
 10. The method of claim 1, wherein said fifth conduit creates aclockwise swirl in said second portion of ballast gas flow.
 11. Themethod of claim 1, wherein said fifth conduit creates acounter-clockwise swirl in said second portion of ballast gas flow. 12.The method of claim 1, further comprising at least one damper situatedon the perimeter of said fourth conduit, wherein said at least onedamper allows the ratio of said first portion of ballast gas flow andsaid second portion of ballast gas flow to be varied.
 13. The method ofclaim 12, wherein at least three dampers are spaced equidistant aroundthe perimeter of said fourth conduit.
 14. The method of claim 12,further comprising sensing devices situated in said first conduit, saidsecond conduit, said third conduit, on said at least one damper, and inthe recycled flue gas stream.
 15. The method of claim 12, wherein saidsensing devices are connected to an automatic control system.
 16. Themethod of claim 1, wherein said substantially pure oxygen is preheatedprior to introduction into said first conduit.
 17. The method of claim1, wherein said substantially pure oxygen is preheated prior tointroduction into said third conduit.
 18. The method of claim 1, whereinsaid second stream, further comprises a secondary fuel stream.
 19. Themethod of claim 18, wherein said secondary fuel stream is selected fromthe group consisting of fuel oil or fuel gas.
 20. The method of claim18, wherein said secondary fuel stream comprises process off-gas. 21.The method of claim 1, wherein said first stream and said first conduitare eliminated, and said second stream and said second conduit are thecentremost.